In the case of open source software which is now basis of data and analytical science (Ince, Hatton, and Graham-Cumming 2012)

• Other users need trust
• Check applicable to their systems and data needs
• Installation
• Contribution model
• Exemplar usage

• Git has transformed software development
  • scientific coding (Perkel 2018)
• Language tooling
• http://github.com/r-lib/

library(devtools)
library(usethis)
library(testthat)

pkg_name <- 'TestUtils'
usethis::create_package(path = pkg_name,
                        open = FALSE,
                        fields = list(Description = "TestUtils package",
                                      Title       = "Provides an example of testing",
                                      Package     = pkg_name))

setwd(pkg_name)
usethis::use_testthat()

## ✔ Setting active project to '/Users/hrards/code/DataScienceWorkshop/Workshop2018/presentations/day-2/09_15_Testing_Hypotheses/TestUtils'
## ✔ Creating 'tests/testthat/'
## ✔ Writing 'tests/testthat.R'

tree --charset=ascii TestUtils/tests 

## TestUtils/tests
## |-- testthat
## |   |-- helper-load-data.R
## |   |-- helper-mock-functions.R
## |   |-- setup.R
## |   |-- test-complex.R
## |   |-- test-regression.R
## |   `-- test-simple.R
## `-- testthat.R
## 
## 1 directory, 7 files

cat TestUtils/tests/testthat/test-simple.R

## context("Simple Test")
## 
## test_that("Simple Description", {
##   ## simple test case
##   expect_true(TRUE, label = "TRUE really is TRUE")
##   ## data vs expectation
##   data <- 1:100
##   expect_equal(data, 1:100, label = "data matches sequence")
## })

context("Simple Test")
test_that("Simple Description", {
  ## simple test case
  expect_true(TRUE, label = "TRUE really is TRUE")
  ## data vs expectation
  data <- 1:100
  expect_equal(data, 1:100, label = "data matches sequence")
})

context("Simple Test")
test_that("Simple Description", {
  ## simple test case that will fail
  expect_true(FALSE, label = "TRUE really is TRUE")
})

setwd(pkg_name)
usethis::use_travis()

• Do tests exercise all code?
• library(covr)

setwd(pkg_name)
usethis::use_coverage(type = "coveralls")

• Notebooks are fun / useful
• Notebooks have problems (Grus 2018)
  • order of execution
  • hidden state
  • how do you test / know code is correct
  • dependencies
  • not a text editor

internal_package <- "TestUtils"
devtools::load_all(path = internal_package)

## Loading code

devtools::test(pkg = internal_package)

## Loading code

## Testing code

## ✔ |  OK F W S | Context
## 
⠏ |   0       | Loading more
✔ |   1       | Loading more
## 
⠏ |   0       | Loading more
✔ |   0     1 | Loading more
## ───────────────────────────────────────────────────────────────────────────────────────────────────────────
## test-regression.R:3: skip: More complex
## Empty test
## ───────────────────────────────────────────────────────────────────────────────────────────────────────────
## 
⠏ |   0       | Simple Test
✔ |   2       | Simple Test
## 
## ══ Results ════════════════════════════════════════════════════════════════════════════════════════════════
## Duration: 0.1 s
## 
## OK:       3
## Failed:   0
## Warnings: 0
## Skipped:  1